In the art of thermal ink-jet printing, it is known to provide a plurality of electrically resistive elements on a common substrate for the purpose of heating a corresponding plurality of ink volumes contained in adjacent ink reservoirs leading to the ink ejection and printing process. Using such an arrangement, the adjacent ink reservoirs are typically provided as cavities in a barrier layer attached to the substrate for properly isolating mechanical energy to predefined volumes of ink. The mechanical energy results from the conversion of electrical energy supplied to the resistive elements which creates a rapidly expanding vapor bubble in the ink above the resistive elements. Also, a plurality of ink ejection orifices are provided above these cavities in a nozzle plate and provide exit paths for ink during the printing process.
In the operation of thermal ink-jet printheads, it is necessary to provide a flow of ink to the thermal, or resistive, element causing ink drop ejection. This has been accomplished by manufacturing ink fill channels, or slots, in the substrate, ink barrier, or nozzle plate.
Prior methods of forming ink fill slots have involved many time-consuming operations, resulting in variable geometries, requiring precise mechanical alignment of parts, and typically could be performed on single substrates only. These disadvantages make prior methods less desirable than the herein described invention.
For example, while sandblasting has been used effectively, it is difficult to create ink slot features that are relatively uniform and free of contamination. Photolithography quality depends greatly on surface conditions and flatness, both of which are very much affected by sandblasting.
Further, at higher frequencies of operation, the prior art methods of forming ink slots provide channels that simply do not have the capacity to adequately respond to ink volume demands.
Fabrication of silicon structures for ink-jet printing are known; see, e.g., U.S. Pat. Nos. 4,863,560, 4,899,181, 4,875,968, 4,612,554, 4,601,777 (and its reissue Re. 32,572), U.S. Pat. Nos. 4,899,178, 4,851,371, 4,638,337, and 4,829,324. These patents are all directed to the so-called "side-shooter" ink-jet printhead configuration. However, the fluid dynamical considerations are completely different than for a "top-shooter" (or "roof-shooter") configuration, to which the present invention applies, and consequently, these patents have no bearing on the present invention.
U.S. Pat. No. 4,789,425 is directed to the "roof-shooter" configuration. However, although this patent employs anisotropic etching of the substrate to form ink feed channels, it fails to address the issue of how to supply the volume of ink required at higher frequencies of operation. Further, there is no teaching of control of geometry, pen speed, or specific hydraulic damping control. Specifically, this reference fails to address the issue of precisely matching the fluid impedance of every functional nozzle so that they all behave the same.
A need remains to provide a process for fabricating ink fill slots in thermal ink-jet print-heads in which the fluid impedance of every functional nozzle is precisely matched.